Hot Weather FAQs

A: There are many things you can do to stay comfortable during heatwaves, including having a cool (but not cold) shower, wearing loose, light clothes, hats and sunglasses, staying out of the sun during 11am and 3pm (remember that sun cream!), opening windows and shutting curtains during the day, and of course, it is essential to stay hydrated, so water, water, water! I’d also recommend freezing some damp flannels or a bottle of water for cooling down when becomes oppressive. It’s also very important to check up on elderly and vulnerable people who may be less able to look after themselves. If you live in a town or city, escape to the countryside for a break if you can, as cities tend to be warmer, particularly at night. Indeed, keeping cool at night is key during a heatwave.

Q: How easy is it to predict heatwaves?

A: Heatwaves are periods of prolonged hot, and often humid, weather, relative to normal conditions. They affect large areas, persist for days or even weeks and often bring uncomfortable daytime and nighttime conditions. They are caused by a slow-moving high pressure system and occur in the UK due to the location of the jet stream which is usually north of the UK in the summer, allowing high pressure and persistent, settled weather to develop. These systems are referred to as ‘blocking highs’ as their presence makes it more difficult for other weather systems to move across an area, resulting in extended hot, dry, sunny weather. Forecasters can identify the weather patterns that may result in a heatwave several days in advance, making them a little easier to predict than unsettled weather. The Met Office has a Heat Health Watch warning system that issues alerts – levels 1 to 4 – if a heatwave is imminent.

Q: What is a 'Indian Summer' and how easy is it to forecast them?

A: ‘Indian summer’ is the term used to describe a warm, calm spell of weather in autumn, and is thought to originate from Native American Indians who could use such conditions to continue hunting. Our ability to forecast them is the same as for any heatwave or period of warm weather, and there is no statistical evidence to suggest that Indian summers occur at particular times. Localised, long range forecasts (beyond 5 days into the future) are difficult due to the chaotic nature of the atmosphere. However extended-range forecasts up to 30 days into the future can provide some indication of how the weather might change or vary from normal (i.e. warmer, colder, wetter, drier) but only across the UK as a whole.

Q: Why is a prolonged period of sun often followed by a massive shower in the UK?

A: Heatwaves and prolonged periods of very hot weather often culminate in storms, due to the build-up of heat and humidity – though it isn’t actually as common in the UK compared to the tropics, where heat is always followed by rain. Summer storms develop when the warm air rises, cools and the water vapour in the air condenses into cloud droplets. Under the right conditions, this occurs rapidly, forming large cumulonimbus clouds and ultimately rain showers, thunder and lightning - another of my favourites! It often feels ‘fresher’ after these storms.

Interestingly, you can actually smell rainfall, and the odours are stronger after a dry spell: Ozone - a sharp, fresh aroma - can often be smelt prior to the onset of a rain storm as it is carried down from the upper atmosphere; this is followed by ‘petrichor’ (from the Greek “petros” meaning stone and “ichor” meaning the fluid that flows in the veins of the gods in Greek mythology) the name describing a combination of odours from decomposing plant and animal matter attached to rocks or soil that are disturbed by raindrops; finally, we are left with the musty smell of damp earth, or ‘geosmin’ from bacteria or algae.

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